Voles, and to
a lesser extent mice, are a major problem when they get
going in a hosta garden. They easily reduce a huge clump to a
few small divisions. They are active year round, but damage
from fall to early spring is usually the worst, and they
reproduce rapidly. Voles and mice can be killed with ordinary
mouse traps or poisons, and each method has some reasons to be
careful.

When using traps cover them with a box or bucket to keep ground
feeding birds and other animals away from the traps. When you use
poison baits, you have to be even more careful as they contain a
scent attractant that will draw a lot of animals to them. Dogs are a
particular problem. The safest way to use poison baits is in large
jars with a quarter size hole in the lid, or a similar feeder with a
small opening. Use a block bait that they have to chew pieces off of
and cannot get out of the feeder.
You can protect prize plants with wire baskets, a
method that works very well but is labor intensive and is difficult
for large hostas. Castor oil deterrents receive mixed reviews - some
say they work while others say they don't. Because voles are easy
prey they prefer cover for their activities and don't like operating
in the open. Cleaning up all leaves and debris and removing
evergreen ground covers like pachysandra can go a long way towards
reducing fall and winter damage from voles and mice.